Japanese Patent No. 2936079 (Patent Literature 1) discloses a launching apparatus for underwater payloads, the apparatus including a launch tube in which an underwater payload is loaded and a water supply device that supplies boosted water to the launch tube. The water supply device includes a pneumatically-driven turbine, which includes an impellers rotated underwater to increase water pressure.
U.S. Pat. No. 2,837,971 (Patent Literature 2) discloses a launching apparatus for underwater payloads, the apparatus including a launch tube in which an underwater payload is loaded and a conduit communicating with the launch tube. The conduit is filled with water and a piston is disposed therein. The piston is pneumatically driven to reciprocally move in the conduit, thereby increasing water pressure in the conduit.
The apparatuses using pneumatic pressure as explained above involves conversion of pressure energy of the air into operation energy for actuating the turbine and the piston, while having a possibility of failing to convert a part of the pressure energy into the operation energy. The pressure energy failed to be converted into the operation energy changes to, for example, vibration energy, causing radiation noise.
For the reason, has been proposed an apparatus that increases water pressure by use of an electromagnetic force instead of the pneumatic pressure. For example, U.S. Pat. No. 5,284,106 (Patent Literature 3) discloses an apparatus that passes an electric current through water (seawater) in a conduit to generate an electromagnetic force, which flows the water in one direction to increase the pressure of the water.
The technique for passing the electric current through the water (the seawater) in the conduit to generate the electromagnetic force, however, involves a problem that the electric resistance of the water (the seawater) affects the generation of the electromagnetic force to prevent water pressure from being sufficiently increased. Applying an excessively high voltage for obtaining a large electromagnetic force enough to overcome the electric resistance may involve electrolysis of the water (the seawater) in the conduit.